长江口海域赤潮生态动力学模型及赤潮控制因子研究

STIDY ON HAB DYNAMICAL MODEL AND HAB LIMITATION FACTORS FOR THE SEA AREA ADJACENT TO CHANGJIANG RIVER ESTUARY

基于中日合作长江口海域生态围隔的试验数据，建立了长江口海域六分量赤潮生态动力学模型，并用海上实测数据进行了检验，进而详细讨论了营养盐及光照强度对赤潮形成的影响。结果表明，此次海洋生态围隔试验加入营养盐无机磷所达到的浓度对于诱发该赤潮过程是适宜的。随着初始Ｎ浓度的降低，Ｐ增加到一定程度便不再影响叶绿素浓度分布。当光照为原光照强度的 ５０％时，叶绿素浓度最高可达３５μｇ／ Ｌ。长江口海域发生赤潮无机氮和无机磷营养盐浓度阈值分别为 ４．５μｍｏｌ／ Ｌ和 １．０μｍｏｌ／ Ｌ。该模型结合水动力学模型不仅可以对海洋赤潮现象进行预测及海洋水质环境的总量控制，也可直接应用于海水养殖，对施肥及养殖容量提供理论指导。

From October 10 to 17, 1997, a marine ecosystem enclosed experiment (i.e. mesocosm experiment) was carried out in the Changjiang River estuary area as a part of Sino-Japan cooperation. 25m3 sea water was filled and the initial nutrient concentrations of total dissolved nitrogen, dissolved phosphate and silicon are 24.8μmol /L, 0.65μmol/L, 40.2μmol/L, respechvely. By adding dissolved phosphate concentration to 3.25μmol/L, a Harmful Algal Bloom (HAB or redtide) was successfully induced. Based on the experiment data, a marine HAB dynamical model is developed. The model includes six variables, including three different nutrients, nitrogen, phosphorus and silicon, two groups of photoplanktons, flagellate and diatom, and detritus. Nitrogen and phosphorus are uptake by phytoplankton and added by phytoplankton respiration and regeneration of detritus. Silicon is absorbed by diatom and not added. Phytoplanktons increase by uptake nutrients and decrease by respiration and death. The dead photoplankton are changed to detritus and the later can regenerate nitrogen and phosphate through decomposition. The model results are consistent with available data. The present work analyses the influence of nutrient concentration and light intensity to the formation of HAB. The main results are as follows. (1) The created HAB dynamical model successfully simulates the whole process. The added dissolved phosphorus is enough for strengthening the HAB process. (2) The threshold values of nitrogen and phosphorus concetration for HAB occurence are 4.5μmol/ L and 1.0μmol/L, respectively, for thes area. (3) When surface light intensity is half of mesured sea surface light intensity, the maximum chlorophyll concentration is 35μg/L. When the light intensity is 35% or below, HAB will not occur.